Export the function to shorten file paths from the terminal package so
that it can be used in the `trace` subcommand.

Fixes #312

Print and set need to receive their argument unsplit to support
complex expressions

The new contents of api.Variable are documented in
proc/variables.go.

Implements #243

Three locations are returned for goroutines: its current location,
its current location excluding unexported runtime functions and
the location of its go instruction.
The command 'goroutines' takes a new parameter to select which
location to print (defaulting to current location w/o runtime)

This adds support for breakpoints statistics

Fixes #247

If an optional linespec argument is passed to clearall command then only
breakpoints matching this linespec will be cleared.

Behavior of clearall command without arguments hasn't changed.

The 'source' command reads the file specified as argument and executes
it as a list of delve commands.
Additionally a flag '--init' can be passed to delve specifying a file
containing a list of commands to execute on startup.

Issue #96

Fixes #257

Support for dumb terminal

Fixes #252

set <variable name> <value>

Replace function with a stdlib implementation.

Default numeric argument now simply represents the depth. If you would
like to see the stack trace of another goroutine, use `goroutine <id> bt`.

stack command: -full flag prints local variables and arguments of all the functions on the stack trace

The shortening of file paths is purely a terminal UI concern. Move that
code to the presentation layer, and remove from the service layer.

Without arguments, `list` displays source around the current context.  A
linespec argument can be taken to display source around that location.

Fixes #58

There's no reason to hang a bunch of commands off of the `info` command.
Promoted all commands to be top level.

Breakpoints, tracepoints, etc.. take a location spec as input. This
patch improves the expressiveness of that API. It allows:

* Breakpoint at line
* Breakpoint at function (handling package / receiver smoothing)
* Breakpoint at address
* Breakpoint at file:line
* Setting breakpoint based off regexp

Fixes #182

This makes parsing by external tools much easier.
It is consistent with pdb.